Long Term Evolution (LTE) is an evolution of the Third Generation Mobile Communication (3G). It improves and enhances the radio interface technologies of 3G, using Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) as sole standards of its wireless network evolution. LTE can provide 150 Mbit/s peak rate of uplink and 300 Mbit/s peak rate of downlink in 20 MHZ spectral bandwidth. Meanwhile, LTE improves the performance to cell-edge users, increases cell capacity and decreases system delay. Compared with 3G, LTE has advantages of high communication rate and spectrum efficiency, low wireless network delay, continuous area coverage and downward compatibility. However, the implementation of LTE requires a high-level design for User Equipment (UE) terminal, such as high baseband chip's ability to demodulate a downlink channel in a terminal and as little as possible memory space taken in the baseband chip.
In the existing TD-LTE systems, data sent from a base station to a UE includes information carried in multiple channels, such as Physical Broadcast Channel (PBCH), Physical Control Format Indicator Channel (PCFICH), Physical Hybrid ARQ Indicator Channel (PHICH), Physical Downlink Control Channel (PDCCH) and Physical Downlink Shared Channel (PDSCH). Relations among the above channels are as follows: information sent on the PBCH is broadcast information, information in the PCFICH indicates demodulation of the PHICH and the PDCCH, and demodulation information in the PDCCH indicates demodulation of the PDSCH.
Referring to FIG. 1, a baseband chip in a UE may include a FFT (Fast Fourier Transform) processor 11, a FFT buffer 12, a MIMO demodulator 13, a channel estimator 14, a CHE (CHannel Estimation) data buffer 15, a MIMO buffer 16, a RE (Resource Element) data de-multiplexer 17, and buffers and decoders corresponding to each of the above channels. The buffers corresponding to each of the above channels may include a PBCH buffer 181, a PCFICH buffer 182, a PHICH buffer 183, a PDCCH buffer 184 and a PDSCH buffer 185. And the decoders corresponding to each of the above channels may include a PBCH decoder 191, a PCFICH decoder 192, a PHICH decoder 193, a PDCCH decoder 194 and a PDSCH decoder 195.
Referring to FIG. 1, after the UE receives data (including a plurality of OFDM symbols) from the base station, the FFT processor 11 processes the OFDM symbols firstly to form FFT data. The FFT data are stored in the FFT buffer 12. Thereafter, in order to demodulate received data, MIMO demodulating need to be performed on received data and MIMO demodulator 13 extracts channel part in the received data to process it. Meanwhile reference signals in the FFT data are extracted and processed by the channel estimator 14 to obtain channel parameters (channel estimation data), so that a channel estimation data matching with an OFDM symbol are input into the CHE buffer 15. Then the demodulated RE data output by the MIMO demodulator 13 are stored in the MIMO buffer 16. Finally, the demodulated RE data are distributed into buffers of each channel through the de-multiplexer 17 of RE data until the accumulated RE data (being soft-bit data after demodulation) meets a requirement of starting decoding. The decoders 191 to 195 corresponding to each channel perform decoding on the demodulated RE data distributed in each channel.
According to the protocol 3GPP TS 36.211 V8.7.0, a PDCCH has following characteristics different from other channels. Soft-bit data in the PDCCH are distributed in N OFDM symbols in the head of each subframe, wherein the value of N may be 1 to 3 and N is an integer. Furthermore, at the base station, the encoded PDCCH as a whole is interlacedly distributed in the RE data of the N OFDM symbols.
Referring to FIG. 2, soft-bit data in the PDCCH are distributed in OFDM symbol 1, OFDM symbol 2 and OFDM symbol 3, namely, N=3. In the existing methods, during the UE demodulating PDCCH, in order to fill the soft-bit data into a PDCCH buffer in sequence at a time, 3 OFDM symbols need to be cached in the PDCCH firstly. Then RE data are extracted from the OFDM symbols according to interleaving and mapping relations to demodulate. Since CHE data matching with the OFDM symbols are needed during demodulating the RE data, N OFDM symbols and the CHE data matching with the symbols needs to be cached in a baseband chip according to the conventional method, which occupies a lot of memory space.
More information relative to a method for demodulating a downlink channel in a TD-LTE system may refer to US patent publication NO. US2010284347A1 entitled “METHOD FOR ACQUIRING RESOURCE REGION INFORMATION FOR PHICH AND METHOD OF RECEIVING PDCCH”, however, which still leaves aforementioned problems unsolved.